Keywords

1 Introduction

Lagoon systems, present on 13% of coasts around the world, are ecosystems of high primary productivity constantly under the threat of a varied of anthropic activities. They are shallow bodies of water, generally parallel to the coastline, which may be connected to the ocean by one or more tidal channels, remaining open, at least intermittently (Kjerfve 1994). The shapes and dimensions of lagoons are directly related to the pre-existing coastal morphology, the way in which sand barriers develop and the action of erosional and depositional processes since the beginning of their formation. The variables related to geological, hydrological, climatic and ecological factors are equally important in the formation and evolution of such environments (Bird 1994). A lagoon normally presents low influx of fresh water and high salinity due to the predominance of evaporation over precipitation (principal mechanism introducing fresh water), the overwash process and the entrance of seawater through the tidal channel. Its hydrodynamic is little influenced by currents and waves, due to the presence of the barrier minimizing interaction with the marine environment (Davis Jr. and Fitzgerald 2008). In general, coastal lagoons work as traps of sediment derived from: (1) internal continental shelf and shoreface, which supply sand and gravel to the lagoon system; (2) aeolian processes, especially in dry climate areas; (3) fluvial inputs, which transports sediments of various sizes, generally deposited close to the internal margin of the lagoon; (4) chemical, biological and biogeochemical processes, which occur through physical and bio-induced precipitation of minerals (Davidson-Arnott 2010). As such, lagoons present rapid sedimentary filling on the geological time, on a scale of thousands of years. When filled, lagoons form extensive closed areas on coastal plains. This infilling is directly related to sediment retention efficiency; to the rate of sea level variations, in response to global climate changes and to local tectonics; with lagoons also being filled by anthropogenic activities (damming of rivers, water pumping, soil use and occupation, etc.) (Kjerfve 1994; Bird 1994). Normal lagoon sedimentation rates vary between 30 and 40 cm per century according to Shepard (1953) or between 1 and 6 mm per year according to Nichols (1989).

On the coast of the state of Rio de Janeiro (Fig. 1B and C) there are lagoons of various dimensions occupying different positions on the coastal plain. The most internal lagoons are larger and are located between the Precambrian basement and, almost always, to the back of the Pleistocene barriers, such as the Jacarepaguá and Rodrigo de Freitas lagoons, in the city of Rio de Janeiro; Piratininga and Itaipu, in Niterói; Maricá, Guarapina and Jaconé, in Maricá; Saquarema and Araruama (Turcq et al. 1999). These lagoons were formed in the Pleistocene by the closure of old bays and they were flooded during the Holocene Transgression (Turcq et al. 1999). This Holocene transgression event enabled the formation of a new lagoon-barrier system confining a series of smaller lagoons in the depression between barriers (Ireland 1987; Turcq et al. 1999; Pereira 2001; Silva 2011; Silva et al. 2014a, b, c).

Fig. 1.
figure 1

(A, B and C) Location of the study area, (D) location of sample points and acquisition of bathymetric profiles in the Maricá Lagoon, Southeastern Brazil.

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Many of these lagoons are degraded and eutrophic, such as Araruama (Oliveira et al. 2011), Rodrigo de Freitas (Domingos et al. 2012) and those of the Jacarepaguá lagoon complex (Sampaio 2008; Gomes et al. 2009; Gomes 2011). Some have suffered a decrease in water surface due to rapid sedimentary filling up and landfill (Resende and Silva 1995; Lavenére-Wanderley 1999; Batista et al. 2003); or, land-use change effect on their surroundings through the construction of engineering work, especially that associated with property speculation and a lack of urban planning.

The objective of the study is the characterization of the geomorphology and sedimentary facies of the Maricá Lagoon in Southeastern Brazil (Fig. 1), as well as the understanding of the coastal processes involved. The methodology of the present research is based on the acquisition of bathymetric and sedimentary data from the lagoon margins and bottom for various analyses. Although a number of studies have been carried out on lagoon systems in the Fluminense area, the Maricá Lagoon, despite its size and geological importance, is still poorly known. Thus, the present study aims to improve knowledge on this environment. It may also assist in the adoption of coastal management measures, which are more and more necessary as a result of the tendency of population concentration on the lagoon margins, especially on the Maricá coast.

2 Study Area

The Maricá Lagoon (Figs. 1 and 2) is located around 50 km to the east of the city of Rio de Janeiro and is approximately max length and width are 6.3 km and 4.5 km respectively. It has an area of around 19 km2, a maximum water-depth of around 2 m and a flat bottom in the shape of a plate (Barbiére 1985). It is the largest and most internal lagoon in the Maricá-Guarapina system (Fig. 1C). The lagoons are connected by channels, forming a single lagoon system, with an area of around 37 km2, which is connected to the ocean by the Ponta Negra channel constructed at the Guarapina lagoon in 1951 through a government sanitation program (Oliveira et al. 1955; SEMADS 2001). This channel reduced the water level of the entire lagoon system (SEMADS 2001). There is also the Costa Canal, which extends from Maricá lagoon to Itaipuaçu beach (to the west of the study area), providing drainage of the coastal plain. Maricá lagoon presents the lowest salinity, varying between 0 and 18‰, depending on the meteorological conditions and the length of time the Ponta Negra channel remains open (Guerra et al. 2011; Kjerfve and Knoppers 1999). This lagoon is part of the Hydrographic Basin of the Maricá Lagoon System, in an area of 330 km2, and receives fluvial input from small streams (Imbassaí, Itapeba, Buriche, Cancio e Cunha), the São Bento Canal and the Mumbuca River (SEMADS 2001).

Fig. 2.
figure 2

Lagoon-barrier systems formed in the Pleistocene (Maricá Lagoon) and Holocene (see Fig. 1C) on the south margin. Photo: Roselly Pellegrino, 2009.

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The geomorphology of the Maricá coastal plain is characterized by the presence of cliffs formed by Precambrian rocks (Coe Neto et al. 1986) and two lagoon-barrier systems (Figs. 1 and 2). One system was formed in the Pleistocene, at least 120.000 years ago (Turcq et al. 1999; Silva 2011; Silva et al. 2014b, c), consisting of the Maricá, Barra, Padre and Guarapina lagoons (Fig. 1C), distributed parallel to the coast, and of the Pleistocene Barrier located to the south of these lagoons. The other was formed in the Holocene and is composed of a series of small filled lagoons and a Holocene Barrier (Fig. 2; Silva et al. 2014a, b, c).

Geological evolution of the Maricá lagoon-barrier system was mainly influenced by variations in sea level (Silva et al. 2014b, c). The sedimentary succession, with a maximum thickness of around 27 m was divided into three depositional sequences, each composed of a muddy unit alternating with a sandy unit: the Pleistocene Coastal Sequence I, the Pleistocene Coastal Sequence II (dated between 48,000–45,000 years cal BP) and the Holocene Coastal Sequence (8,500 years cal BP) (Silva et al. 2014b, c). Silva et al. (2014b, c) considered that the Maricá Lagoon may be associated with the extensive muddy unit identified at the base of the Pleistocene Coastal Sequence I, and its formation may have started around 120,000 years BP, corroborating the information provided by Turcq et al. (1999). Analyses of formanifera carried out by Bruno (2013) on cores of up to 1.78 m in length and close to the Southeastern margin, indicated 2 moments in the Holocene history of the Maricá Lagoon: around 2740−2460 years cal BP, this lagoon had a connection to the sea and its hydrodynamic varied from medium to high; from between 1040 and 970 years cal BP until the present day, a low hydrodynamic and low salinity predominate in response to closure of the referred channel.

The Maricá coast is dominated by waves from the south eastern quadrant, associated with good weather conditions, and from the south and southeast, during the occurrence of storms caused by the occasional passage of cold fronts, when waves can reach 3 m high at breaking point (Muehe 1979; Silva et al. 2008a). These waves occasionally overcome the barrier during storms of greater magnitude, depositing sediments directly in the lagoons (Silva et al. 2008b), as occurring at the Maricá Bar (at the eastern edge of the Maricá lagoon), which is a section where the barrier is narrower in comparison to adjacent areas. It is also in this section where manual opening of the channel through cutting of the barrier historically occurs, enabling connection of the Barra Lagoon with the sea. (Oliveira et al. 1955; Pinheiro 2015). On this coast, the maximum spring/neap tide amplitude is always below 1.5 m (DHN). The wind regime is determined by the South Subtropical Anticyclone, with the predominant occurrence of winds from the east and north-east quadrants (Amarante et al. 2002). When the winds are from the south-east, south or south-west, generated by polar air masses from the south, they become more intense (CPTEC, INPE).

There are different types of use and occupation on the margins of the Maricá Lagoon. The most well-preserved sections correspond to the south and west margins, as they are within the limits of the Maricá EPA (Environmental Protection Area) (Fig. 1C); the north and east margins are urbanized (Pereira and Mello 2011).

3 Materials and Methods

The morphology of the bottom of the Maricá Lagoon was characterized through the acquisition of around 30 km of bathymetric data along 11 profiles perpendicular and transversal to the coastline (Fig. 1D). The field work was carried on in August 2015, a year with low rain precipitation. For the bathymetric survey a SONARMITE V3 echo sounder from OHMEX Instrumentation, fixed to the side of an inflatable boat, was used. The transductor of the equipment was positioned at a depth of 0.4 m below the water line, this value being subsequently added to the acquired depths. The data was georeferenced with the assistance of a DGPS (Differential Global Positioning System), GTR-G2 model from TechGeo, fixed to the same rod as the echo sound transductor. Depth data was also collected manually with the assistance of a survey line where navigation was not possible. The data collected with the DGPS and the echo sounder were automatically associated using HYPACK 2013 software; subsequently, the SIG ArcMap 10.3 was used for interpolation, digital land model (DLM) generation and final layout of the bathymetric map at a scale of 1:15,000.

Lagoon floor sediments were collected (Fig. 1D) with a Van Veen sampler from inside the Maricá Lagoon along the margins, using a container to collect only superficial sediment. The Van Veen sampler penetrates between 6 and 8 cm. This interval represents the same depositional unity with no indication of changes in the sedimentary processes, and the sedimentary facies is the best evidence for that. The 72 samples were analyzed for grain-size at the Sedimentology Laboratory of the Geosciences Institute of the Fluminense Federal University (Universidade Federal Fluminense - UFF). The granulometry was carried out using laser diffraction methodology (for finer sediments) and digital imaging analysis methodology (coarser sediments). In the laboratory, the samples were initially frozen, then freeze-dried; around 50−60 g were weighed and washed in a 0.063 mm sieve to obtain the sand and silt/clay fraction percentages. The samples were then weighed again, frozen and subsequently freeze-dried. For fine sediment granulometry a Malvern Mastersizer 2000 was used, in accordance with the following procedure in the sample treatment stages: weighing of 3 g of sediment, which was placed in falcons, addition of deflocculant solution (45.7 g of sodium hexametaphosphate diluted in 1 L of distilled water), samples were mixed during 48 h in an electric agitator. Granulometry of the coarse sediment was done based on the Particle Size and Shape Analysis System with CAMSIZER Digital Image Processing, after quartering of the samples until reaching a weight of approximately 25 g. The data were processed and classified using the GRADISTAT 2007 program (Blott and Pye 2001), which calculated grain-size parameters based on Folk and Ward (1957) and the granulometric classification according to Wentworth (1922). After the analyses, 26 representative samples of the lagoon margins were selected, for morphoscopic analysis (rounding and luster) based on the classification proposed by Folk (1980) and observations relative to sediment composition. The samples were collected in the most preserved areas to avoid places where human impact is important. Morphoscopy was carried out through counting and characterization of 100 grains of quartz from the predominant fraction of each selected sample, using a binocular magnifying glass with illumination by reflection. The images were captured through the ToupView program. This stage was carried out at the Nature Dynamics Laboratory (Laboratório de Dinâmicas da Natureza - LABDIN) of the State University of Rio de Janeiro (Universidade do Estado do Rio de Janeiro - UERJ).

Lagoon water level measurements were carried out every fifteen minutes during fieldwork, with the objective of verifying fluctuations resulting from tidal influence on the Maricá Lagoon. For this, a vertical measurement ruler located around 50 m from the lagoon margin was used, with the aim of minimizing the interference of waves.

4 Results and Discussions

4.1 Morphology of the Maricá Lagoon

The Maricá Lagoon is particularly shallow, with a maximum depth of around 2 m, presenting a predominantly flat bottom (Fig. 3). Depth increases gradually from the margins of the lagoon down to 1.5 and 2 m. The change from the margins to the more central area of the Maricá Lagoon occurs where sandy sediments change to sandy muddy. The submerged section of the margin extends an average of 400 m (north) and 250 m (south) from the water line. Depth then increases gradually toward the more central areas of the lagoon (Fig. 3), which is almost totally flat, except in the areas where there are rocky outcrops.

Fig. 3.
figure 3

Bathymetric map (A) and profiles (B) associating manually acquired data with the echo sounder. Adapted from Silvestre et al. (2017).

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The bathymetric profiles (with north-south orientation – Fig. 3) indicated a morphology with little change, varying only in inclination, which is greater at the margin closer to the southern barrier than to the inner northern margin. The submerged section of the northern margin is smoother, where the depth of 0.5 m appeared at a distance of 60 to 110 m from the water line; increased to 1 m between 130 and 250 m and reached a maximum depth of 1.5 m between 320 and 720 m from the water, where the margin-bottom transition occurs. At the margin with the southern barrier, the increase in depth occurs more rapidly. A depth of 0.5 m appears at 30 m from the water line, except in the central-south section, where the same depth occurs until 160 m, due to the existence of a protuberance on the margin, which suggests the presence of a washover fan deposit or an ancient flood-tidal delta; reaching a depth of 1.0 and 1.7 m at 160 and 300 m from the water line.

Depth around the Mumbuca River increased slowly up to 1.4 km from the water line. The water column is 0.5 m at around 200 m from the mouth, reaching 1 m at 540 m and 1.25 m at 1.4 km. These values indicated high sedimentation rates in the area causing the formation of a lagoonal delta (Figs. 3 and 4), demonstrated by the morphology and shallower bottom in from of the river mouth, different to the adjacent areas. Other smaller deltas appear to be associated with streams emptying at the northern margin, also contributing to sedimentation of the area.

Fig. 4.
figure 4

- Sediments from the floor and margins of the Maricá Lagoon examined under binocular microscope: (A and B) quartz-rich coarse sand (q) with shells and feldspar (f) at the south margin and (C) at the west margin; (D) medium sand at the east margin, with heavy minerals (hm); (E) fine sand with micas (m) at the north margin; (F) silty sand with shells (arrow); (G) sandy silt with (H) bioturbation and (I) gravel with mica and feldspar.

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Comparison between the manually acquired depths and those of the echo sounder (Fig. 3) presented small differences. In general, the results obtained with the echo sounder are slightly deeper than the manual survey. These differences of a few centimeters (10−20 cm) may have been generated by data acquisition occurring on different days and, consequently, being subject to fluctuations in the water level caused by changes in the hydrological regime or by waves. More specifically, in areas close to the north and east margins, the bathymetric map did not present depth distribution in the same coastal configuration, differently to the southern sector. This occurred as a result of the absence of data for a more representative interpolation of the shallower areas, which are generally of difficult access.

The morphology of the Maricá lagoon floor and the bathymetry in the present study (Fig. 3) corroborated the description made by Barbiére (1985), in which the author characterized the lagoon bottom as smooth and in the form of a plate, with a maximum depth of around 2 m in the central-south area. A study carried out by Oliveira et al. (1955) indicated that the central section of the lagoon presented a depth of around 2.5 m; between 0.2 and 1.1 m around the mouth of the Mumbuca River; and variations between 1.8 and 3.5 m in the area between Ponta do Boqueirão and the Zacarias fishing community. The depths presented by Oliveira et al. (1955) are slightly deeper than those identified in the present study as well as in Barbiére (1985), which may be related to sedimentation of the lagoon, especially between Boqueirão Point and the fishing community associated with the Mumbuca River delta. However, the absence of bathymetric data (in the case of Barbiére 1985) and data on meteorological conditions in which the data were acquired (in both studies cited above), makes it impossible to compare, more conclusively, the depths recorded at distinct moments. It is important to highlight that in periods of heavy rainfall, the water level of the Maricá Lagoon tends to increase, despite the connection with the other lagoons through channels. In a recent field survey (January 2016) carried out during a period of intense rains (total accumulation of 850 mm for the month), an increase of 0.5 m was found for the level of the lagoon.

The sedimentation rate for the Maricá Lagoon was measured through 210Pb isotope analyses, resulting in 0.28 cm/year close to the São Bento Canal, 0.36 cm/year close to the mouth of the Mumbuca River (Fernex et al. 1992) and 0.4 cm/year in the central area (Marques et al., 1995). Considering the sedimentation rate proposed by Marques et al. (1995) and the depths found in the present study, the central section of the lagoon should increase around 40 cm in sediment thickness over the next 100 years, reducing the depth to 1 to 1.5 m approximately. The sedimentation rates of other Fluminense lagoons showed significant variations in their respective depositional sub-environments (marginal areas and lagoon floor). Commonly, the values are higher for the margins and lower for the deepest central area, where deposition occurs through settling of fine particles. The Piratininga Lagoon presented a sedimentation rate of 0.13 cm/year in its central section for the last century (Resende and Silva 1995), while the Itaipu Lagoon showed a rate of 0.28 cm/year at the margin of the lagoon (Lavenère-Wanderley 1999). In the Rodrigo de Freitas Lagoon (RJ), sedimentation is higher and corresponded to 0.75 cm/year in the central area (Loureiro et al. 2012). Shepard (1953) considered that the normal rate of lagoon sedimentation is between 30 and 40 cm per century. In which case, only the identified values for the Maricá and Itaipu Lagoons are within normal lagoon sedimentation rates; the Piratininga Lagoon has a much lower rate and the Rodrigo de Freitas Lagoon has a much higher rate in relation to the expected.

4.2 Sedimentary Facies of the Maricá Lagoon

The sediments in the Maricá Lagoon (Fig. 4) are mainly silty sand (37.5%) and sand (37.5%), followed by sandy silt (21%). Gravelly sand (3%) and sandy gravel (1%) (Fig. 4) also appeared in smaller proportions. The mud fraction is mainly coarse and very coarse silt and clay; very fine and fine sands are dominant, with a considerable amount of shells and shell fragments of various sizes (Fig. 4).

A total of 5 lagoonal facies were identified (Table 1; Fig. 5): sub-rounded sand, angular sand, silty sand, sandy silt and silt/clayey silt.

Table 1. Sedimentary facies and processes in the Maricá Lagoon.
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Fig. 5.
figure 5

Map of the sedimentary facies distribution in the Maricá Lagoon.

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The sub-rounded sand facies (Table 1) occurred on the subaerial and subaqueous south and west margins of the lagoon (Figs. 4A-C, 5 and 6A). These facies are characterized, basically, by coarse granulometry, good rounding and the dull aspect of the sands. Shells of the H. australis gastropod were found in these facies (Silvestre 2018). The sub-rounded sand facies present granulometric characteristics similar to those on the beach of the Maricá EPA, where coarse and medium sands predominate (Silva et al. 2014c). Sediments from the Pleistocene and Holocene Barriers also present similar grain-size characteristics (Silva et al. 2014b), as the Holocene Barrier dunes does (Silva et al. 2012), which are also sources of grains with frost aspect, characteristic of wind reworking; and the washover fan deposits present on the coast (Silva et al. 2008b); the same occurs between the degree of rounding of the sands from this facies and the sands from the coastal plain (Batista 2015). It can therefore be deduced that the barriers have been the main sources of sediment for these lagoonal facies.

Fig. 6.
figure 6

Beaches on the (A) south and (B) west margins of the Maricá Lagoon. (C and D) Waves formed by strong winds on the Maricá Lagoon. Photos: (B) Jornal O Maricá, 2018; (C) Mila Viegas, 2010.

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The processes responsible for the deposition of the sub-rounded sand facies in the lagoon are those commonly observed at times of high energy, such as: strong winds, which carry sands from various barrier environments (beach, dune) and deposit them in the lagoon; processes related to strong swells, when waves remove sand and gravel from the barrier and carry them to the lagoon; and transport through tidal channels. These processes occur today in the eastern section of the study area; and although they do not occur to the west, they may have occurred there also during the active phase of the barriers at this location.

The angular sand facies (Table 1; Fig. 5) are found at the eastern and northern margins (Figs. 4D and 4E), forming the internal lagoon beaches (Fig. 6B). This facies is characterized by heterogeneous grain size, but with a higher concentration of coarse and medium quartz sand, with predominantly angular and vitreous grains. This material presents poor reworking of its grains and was probably transported in an aqueous medium and through river discharge deposited in the Maricá Lagoon (Fig. 1D). Similar sedimentary characteristics found in the present study for the southern and northern margins were also identified by Perrin (1984).

The silty sand facies covers a large part of the lagoon bottom: central-east section, mouth of the Mumbuca River and close to the south and west margins (Table 1; Figs. 4F and 5). The material found to the north of the central-east section, in the extreme west and close to the Mumbuca River presents heterogenous sediments, with a predominance of fine and very fine quartz sand, with sub-angular and vitreous grains. The silty sand facies present slightly different characteristics between the central-east section and close to the south margin (Table 1; Fig. 5); the quartz sand varies from coarse to medium, with shells and shell fragments and sub-rounded, dull grains. These characteristics indicate a more mature sediment than that identified close to the north and west margins. The presence of these proximal facies in the Maricá Lagoon demonstrated that the sandy sediments of the submerged margin are being gradually mixed with silt brought by the rivers, which is deposited at low energy moments (Fig. 5). The waves observed during field work in the Maricá Lagoon (Fig. 6C and D) are sufficiently capable of remobilizing and reworking the sandy sediments at the margins and the muddy sediments at the lagoon bottom, promoting their mixture in these areas.

The sandy silt facies (Table 1; Fig. 4G) are found in the central section of the lagoon, extending to the north-west and south-east. A smaller area in the subaqueous part of the Mumbuca River delta also presents sand silt facies (Fig. 5). The material composing this facies consisted of very coarse silt, very fine sand and clay, dark gray in color and contained on average 13% organic matter (Silvestre et al. 2017). The places where sandy silt facies predominated may represent the limit of the waves and currents activity in the transport and reworking of sandy sediments coming from the rivers (especially the Mumbuca River) during the flooding phase, that is, moments of higher energy followed by calm moments that enable the deposition of muddy sediments from fluvial input.

The silt/clayey silt facies was identified in association with the sandy silt facies, in the central-west area of the lagoon bottom (Table 1; Fig. 5), and it is the finest facies identified in the Maricá Lagoon. This facies is basically represented by very coarse silt and clay, with a very dark gray color and, on average, 12% organic matter (Silvestre et al. 2017). Like the sandy silt facies, these facies also originate from fluvial input, which are deposited by decantation of the mud in areas and moments of lower hydrodynamics. The main fluvial source for this lagoon is the Mumbuca River (Fig. 1D), and the sediments carried by this river are responsible for the construction of a delta (Fig. 3), which extends from the mouth to the central area of the lagoon and has increased significantly since the 1950s (Oliveira et al. 1955).

The low local hydrodynamics have probably favored the concentration of organic matter in the area where the finest facies occurs (sandy silt and silt/clayey silt), similarly to what takes place in the Rodrigo de Freitas Lagoon (Baptista Neto et al. 2011).

5 Conclusions

The Maricá Lagoon maximum depth is 2 m, but it can show variations as a result of heavy prolonged rains, which can elevate the water level by approximately 0.5 m. The lagoon presents a flat floor (except where rocky outcrops exist) with the form of a plate, with a slightly steeper slope on the south face in relation to the north. The transition between the margin and the bottom occurs at 1.5 m deep, where a gradual change from sandy to muddy sediments took place.

The bottom sediments consist mainly of sandy silt and silty sand, composed of quartz and lower proportions of feldspar, micas, heavy minerals, shells and shell fragments. The sediments characteristics (color, grain size, morphology, composition and organisms) collected from the lagoon floor enable the definition of the following lagoonal facies: sub-rounded sand, angular sand, silty sand, sandy silt and silt/clayey silt. The sub-rounded sand facies characterize proximal areas in the lagoon closer to the sea, which receive more mature sediments coming from the barriers. The angular sand facies occur in proximal areas towards the internal side of the lagoon, as the more immature sediments are mainly brought by rivers arriving at the lagoon. The silty sand facies presented slightly different characteristics between sections of the Maricá Lagoon in the more internal areas or near the barriers, but, in general, the association between sand and silt indicated transitional areas between proximal sandy facies and those distal sandy silt in the lagoon floor, suggesting lower hydrodynamics than at the margins. The sandy silt and silt/clayey silt facies covered the central area and the bottom of the lagoon and represented the places with the lowest hydrodynamic. The muddy sediments also presented a higher concentration of organic matter (between 18% and 81%). The factors favoring the accumulation of organic matter in the lagoon are fluvial input, disposal of untreated sewage, low hydrodynamic, the presence of vegetation on the south and west margins and at the lagoon bottom and the proliferation of algae.

Sedimentation in the Maricá Lagoon is subject to the direct influence of the wind regime, which, during storms, can transport sediments from the barriers to the lagoon and also generate waves that can reach heights of over 1 m, which can remobilize sediments at the margins and on the bottom. Today, the interaction between winds, waves and river discharge represents the principal processes controlling on the sedimentary dynamics of the Maricá Lagoon.